1. Field of the Invention
The present invention relates to a relay station for conducting radio communication between two subscriber stations, consisting of a receiver which is capable of being synchronized to the transmitting subscriber station, and a transmitter having a transmitting frequency which has, in relation to the receiving frequency of the receiver, a satisfactorily-large signal-to-noise ratio, as well as an interface connection between the receiver output and the transmitter input for the transfer of useful signals received by the transmitting subscriber station to the transmitter for the purpose of repeated transmission to the receiving subscriber station.
2. Description of the Prior Art
In radio networks there is occasionally the necessity of enlarging the transmitting range of individual subscriber stations belonging to the radio network or, however, due to unfavorable topographic conditions of subscriber stations located in shadow regions, to make possible reliable radio connections to remote subscriber stations. For this purpose, use is then made of a special transmitting-receiving station which can reliably receive a transmitting subscriber station, on the one hand, and in addition, the receiving subscriber station can also, in turn, reliably receive the transmitter of the transmitting-receiving station, hereinafter called a relay station. Relay stations of this type are known, for example, from the German patent 24 02 810 A1.
Since, in the case of such a relay station, the transmitter and the receiver must be at one location, precaution must be exercised to ensure that the electro-magnetic energy radiated by the transmitter cannot become active in the input of the receiver and block the receiver through overdriving thereof. In other words, it must be ensured that, in the case of such a relay station, the receiver and the transmitter always operate at different frequencies whose mutual frequency separation must be selected to be so great that the minimum requirements of the frequency separation to be made here are met.
In the case of mobile radio networks in tactical use, generally special measures must additionally be effected which render the desired radio connections resistant to intentional interference or jamming. In order to achieve this increased interference resistance, as the German patent 32 30 726 A1 points out, for example, it is known to vary the radio frequency in brief time intervals suddenly and in a pseudo-random manner in a larger frequency range. The application of such a frequency hopping method to a radio connection between two subscriber stations pursuant to interconnection of the relay station makes it necessary to subdivide the frequency jumping region, present per se, for the receiver and the transmitter of the relay station into a lower band and an upper band. On the partial connection path between the transmitting subscriber station and the relay station, a pseudo-random radio frequency change in the lower band, and simultaneously such a pseudo-random radio frequency change in the upper band, can then be carried out on the partial connection path between the transmitter of the relay station and the receiving subscriber station. In this manner, the satisfactory separation between the receiving frequency and the transmitting frequency of the relay station is perserved, and also the minimum separation requirements can be observed without difficulty. However, the disadvantage of this solution is that the frequency bandwidth, available per se for the frequency hopping, is respectively cut in half relative to one of the mentioned partial connection paths. The capability to resist interference through such a frequency hopping method is, in particular, proportional to the bandwidth of the available frequency hopping range.